RU2539666C2 - Potential fluidisation device intended for loose material transportation in superdense layer - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: device allowing to transport loose material (12) includes conveyor (3) having lower channel (6) where gas is circulating and upper channel (7) intended for circulation of loose material and the mentioned gas. The mentioned upper channel and the mentioned lower channel are separated by porous wall (5) through which the mentioned gas can pass, herewith into the lower channel, gas is injected under pressure which provides potential fluidisation of the mentioned loose material in the mentioned upper channel. The mentioned upper channel in its upper part is equipped with traverse walls (50) located so that together with the upper wall of the mentioned upper channel they bound at least one dome where pressurised gas bubble (20.1, 20.2) is formed as a result of potential fluidisation pressure generation in the mentioned air duct. At the level of at least one bubble formed in such a way, wall of the upper channel contains fluidising gas removal facility equipped with negative pressure generator (120.1, 120.2) which produces essentially constant negative pressure.

EFFECT: device manufacturing simplification.

20 cl, 6 dwg

Description

The invention relates to a closed potential fluidization device for horizontal or inclined transportation of materials having the properties of bulk solids, capable of transitioning into a fluidized state, from the storage area, at least one feed zone, which are removed from each other, usually several hundred meters .

In particular, the invention relates to a closed potential fluidization device for transporting and supplying “reserve containers” with a bulk material, such as alumina, for continuously supplying said bulk material from a single storage area to a packaging complex, such as a bagging machine, or to a production a complex, such as an extruder or a series of electrolysis cells for fire electrolysis.

By materials capable of going into a fluidized state, we should understand all materials well known to specialists and having a loose form, while their grains have such adhesion and have such a particle size distribution in which the passage of air pumped through the bulk mass at a low speed leads to the disengagement of particles among themselves and to reduce the forces of internal friction. Such materials are, for example, alumina intended for fire electrolysis, cements, gypsum, quicklime or slaked lime, fly ash, coal dust, salt crystals such as calcium fluoride, sodium sulfate, phosphate ..., granules of plastic materials, food products, such like milk powder, flour, etc.

The invention also relates to a device for transporting bulk materials over a long distance, typically greater than one kilometer.

A bulk material transport device, developed and described by the applicant in European patent EP 0179055, provides a continuous supply of solid bulk solids in a superdense phase. It is intended, in particular, for uniform and continuous supply of alumina to the collection and dosage bins located in the upper structure of a number of electrolyzers. It is a potential fluidization device. As with classical fluidization, this device contains between the storage zone and the feed zone at least one horizontal conveyor, called an air duct, consisting of a lower channel for circulating gas, an upper channel for circulating bulk material and gas, both of which the channels are separated by a porous wall through which said gas can pass. Gas enters the lower channel through at least one supply pipe. Unlike what happens with classical fluidization, the bulk material completely fills the upper channel of the conveyor, and this conveyor is equipped with at least one expansion column, partially filled with bulk material, while the height of the suspension of solids / gas balances the gas pressure. This expansion column allows you to create conditions for potential fluidization of bulk material. This material, which is practically not mixed due to the very low pressure of the gas, has the appearance of an ultra-dense layer in the duct.

In order to better understand the nature of potential fluidization, it should be recalled that it is a classic fluidization, usually used for transporting bulk materials and described, for example, in US patent 4016053. The device used for fluidization also contains the above-described duct. The fluidization gas flows under a predetermined pressure p _f into the lower channel, passes through a porous wall, then between the particles of bulk material that are at rest and form a fluidized bed. In contrast to the potential fluidization device described in EP 0179055, the thickness of this layer at rest is much less than the height of the upper channel of the aforementioned conveyor, i.e., in the absence of injection of a fluidizing gas, the bulk material only partially fills the upper channel of the horizontal conveyor. When gas is supplied under high pressure, these particles begin to move and rise, while each of them loses the point of constant contact with neighboring particles. Due to this, the intermediate space between particles increases, internal friction between particles decreases, and these particles go into a state of dynamic suspension. This leads to an increase in the initial volume of bulk material and, consequently, to a decrease in bulk density, since a suspension of the solid phase in the gaseous phase is formed.

Thus, the bulk density is lower than the bulk density for potential fluidization described in document EP 0179055, which refers to the superdense phase. Typically, the term "dense phase" is used in pneumatic transport under high pressure. The superdense phase is characteristic of potential fluidization. For example, in the case of Al ₂ O ₃ alumina, it is believed that the solid / gas ratio is from about 10 to 150 kg Al ₂ O ₃ / kg of air during pneumatic transportation in the dense phase and from 750 to 950 kg Al ₂ O ₃ / kg of air during transportation with potential fluidization in a superdense phase. Thus, the superdense phase allows the transport of solid bulk material at very high solid / gas concentrations much higher than the dense phase during pneumatic conveying.

In the case of potential fluidization, even in the absence of gas injection, the bulk material almost completely fills the upper channel. When gas is supplied to the lower channel, the compensation column is partially filled with bulk material occupying the upper channel at a gauge height that balances the pressure p _f and prevents an increase in the gaps between the particles. Due to this, the compensation column prevents the fluidization of the bulk material present in the horizontal conveyor, and forces the said material to take the form of an ultra-dense layer with potential fluidization. In addition, since the intermediate distance between the particles does not increase, the permeability of the medium with respect to the gas entering under pressure pf is very low and limits the gas flow to a very small flow rate. The passage of this gas stream with a small flow through the compensation column is called "degassing". For example, a circulating gas velocity corresponding to a fluidization pressure p _{f of} 80 mbar and leading to fluidization of bulk alumina is about 33.10 ⁻³ m · s ⁻¹ in the device described in US 4016053, whereas in a potential fluidization device according to EP 0179055 the velocity of the circulating gas is only 4.10 ^-3 m · s ^-1 . This speed is too slow to cause alumina fluidization throughout the conveyor.

Thus, there is no fluidization as such, but we can talk about potential fluidization: if there is no constant circulation of material in the duct, then the flow looks like successive shifts as soon as the need for bulk material appears, for example, when the level of the feed zone drops below the critical values. Indeed, when the continuous flow of material in the feed zone becomes such that the level of the material decreases and falls below the opening of the feed channel, a certain amount of bulk material leaves the channel, creating a “void” that fills due to shedding of material, which leads to another shedding at the entrance and is reproduced, thus, from one to the other in the duct, rising to the storage bunker.

The potential fluidization device for transportation in an ultra-dense layer described in document EP 0179055 is widely used, in particular, for supplying electrolytic cells of modern aluminum production plants with fire electrolysis. EP-B-1086035 describes an improvement of the previous device, in which the upper part of the upper duct channel in some places is equipped with barriers, for example, in the form of steel sheets perpendicular to the wall of the upper part, which contribute to the creation and long-term storage in the upper part of the upper channel the duct of adjacent gas bubbles, inside of each of which bubble pressure acts when fluidizing gas is supplied to said duct under the pressure of potential fluidization. Indeed, the applicant has found that the creation of gas bubbles under pressure provides a more stable operation of the duct.

In international patent application WO2009 / 010667, the applicant specified the optimal conditions under which such a device can be used with minimal risk of segregation of bulk material during transportation.

Having convinced himself of the successful and practically systematic use of this type of device, in particular in most modern aluminum electrolysis plants, the applicant decided to further improve the solution associated with transportation in the superdense phase. In particular, he conducted tests to check the limits of the system in order to clarify important parameters, which, on the one hand, make the use of such air ducts more flexible and, on the other hand, simplify their design and manufacture.

The first object of the invention is a device that allows the transport of bulk material between the feed zone, usually the storage zone of the aforementioned bulk material and at least one feed zone, containing a conveyor called an “air duct”, which contains a lower channel for gas circulation, and an upper channel for circulating bulk material and said gas, wherein said lower channel and said upper channel are separated by a porous wall through which can pass l said gas, wherein the lower channel is connected to a gas supply pipe configured to supply said lower channel with pressurized gas, which provides a potential fluidization of said bulk material in said upper channel, and which will hereinafter be called “potential fluidization pressure” or simply “ fluidization pressure ", while the upper channel is equipped in its upper part with transverse walls that form an obstacle to the circulation of the said gas and the aforementioned bulk material, wherein said walls are arranged in such a way that together with the upper wall of said upper channel they form at least one space in which a gas bubble forms under pressure as a result of creating a potential fluidization pressure in said duct, wherein the pressure in said the bubble is called "bubble pressure", wherein said device is characterized in that at least one bubble, and preferably at the level of each bubble, the upper wall of the channel is equipped with a fluidizing gas removal means connecting the said bubble with the external environment, usually with ambient air or with a device designed to treat gases (gas processing center or “CTG”) trapped above the electrolysers, and containing means for creating a vacuum, which creates essentially constant depression or loss of pressure. This pressure loss is determined so that if the gas is removed to an external environment where the pressure is substantially constant (for example, ambient air at atmospheric pressure), said bubble pressure is maintained substantially constant between the fluidization pressure and said external pressure Wednesday.

The applicant conducted laboratory tests to verify the operating limits of the system described in EP 1086035. In particular, some tests were carried out to clarify the phenomena that occur in the compensation column. The air duct, which is a fluidization column above which the compensation column is located, contains walls, one of which was made transparent, which made it possible to track the behavior of bulk material in the upper channel and in the compensation column. Thus, it was found that the turbulent mode in the compensation column leads to significant fluctuations in the upper level of bulk material present in the compensation column, and that this leads to a violation of the layer in the duct near the said compensation column. In addition, an unloading valve was installed on the upper wall of the upper channel in order to be able to change the pressure in the bubble in the widest possible range of values without changing the operating mode of the fan, which feeds the lower channel with fluidizing gas. During the tests, the applicant unexpectedly discovered that the opening of the discharge valve allows to stabilize the upper level of bulk material present in the column in the sense that the amplitude of the change in the height of the upper level of the column is significantly reduced. In other subsequent tests designed to simulate an air duct equipped with barriers separating several bubbles, the applicant used this idea of equipping the upper part of the upper channel with an unloading valve: he unexpectedly discovered that this helped to prevent the appearance of large-amplitude oscillations on the layer surface with potential fluidization in the upper channel.

Thus, having equipped at the level of each bubble the upper part of the upper duct channel with an unloading valve, the applicant found that the pressure loss provided by this valve allows extremely effective stabilization of bubble pressure, the level of bulk material in the compensation column and, in general, the flow of bulk material. Based on this conclusion, the applicant set himself the task of finding out whether the use of such discharge valves would reduce the number of expansion columns and even completely abandon them in the case when they can fully fulfill the role assigned to expansion columns, that is, the role of pressure balancing p _f gas potential fluidization.

During these last tests, the applicant was able to confirm his expectations: the duct can work without expansion columns to transport bulk material in the superdense phase due to potential fluidization: it is enough to replace the said expansion column with a discharge valve or any means that creates an essentially constant vacuum, predetermined the value of which allows, at a fluidization pressure p _f in the lower channel and at a substantially constant external support pressure p _a bubble pressure p _b in a stable value in the optimal range of values for the flow of bulk material, in the range from p _a to p _f .

In other words, the device in accordance with the invention comprises, at the level of at least one bubble, and preferably at the level of each bubble, a means of creating a vacuum, whether or not it is equipped with a compensation column. In the first case, the aforementioned means of creating a vacuum mainly plays the role of stabilizing the level of suspension (bulk material + gas), which is located in the compensation column and which balances the fluidization pressure. In the second case, it also plays the role that was assigned to the compensation column. In addition, in the absence of a compensation column, it makes it possible to achieve a higher bubble pressure with an identical pressure source and thus increase the conveying capacity of the conveyor with the same energy consumption. Of course, the bubble pressure is higher, but cannot reach the level of fluidization pressure, since, on the one hand, there is a loss of gas pressure as it passes through the porous wall, and, on the other hand, pressure loss when it passes through the particles in the fluidized bed.

The first case (the presence of a compensation column) corresponds to the improvement of existing industrial systems or the use of conveyors with a much smaller number of compensation columns compared to conventional practice, for example, conveyors, characterized in that they are equipped with a compensation column every 20 meters, instead of having a compensation column every 6 meters The second case corresponds to the use of new conveyors, characterized by the complete absence of expansion columns.

An advantage of the claimed device is the ability to control the level of bubble pressure and the rate of exit of the fluidizing gas. In the compensation column, the role of the pressure gauge is played by a suspension of bulk material / gas: due to its density and its volume (represented by the height of the column), it balances the pressure in the upper channel. The manometric effect of the material in the compensation column was the main factor explaining the widespread use of this type of device, but its disadvantage is the dependence of the bubble pressure on the fluidization pressure, so the bubble pressure could be changed only by changing the fluidization pressure. By eliminating the compensation column and replacing it with a means that creates a controlled vacuum, adjustable to a predetermined value, you can directly affect the bubble pressure without changing the fluidization pressure, so the conditions for using the conveyor are much more flexible.

Preferably, in particular, in order to avoid contamination of said external environment with small particles of granular material entrained by the removed fluidizing gas, the said fluidizing gas removal means should also be equipped with at least one solid / gas separation device. It is also obvious that the solid / gas separation device in itself creates a pressure loss, which must be taken into account in order to determine the corresponding dimensional parameters of said rarefaction means.

Under the means of creating a vacuum should be understood

a) a simple hole or "diaphragm" adjacent to the envelope of the volume occupied by the bubble, for example, which is made in the upper wall of the upper channel and the diameter of which ensures a pressure loss corresponding to the desired bubble pressure; said opening may be an inlet of an outlet pipe discharging said gas into said external medium;

b) an unloading valve containing a hole with a variable diameter, which allows you to change the pressure loss of the gas during its removal, that is, to change the bubble pressure;

c) venturi pipe;

d) at least one solid / gas separation device that is often necessary in this field of application, for example, a cyclone-type device, where the gas containing solid particles enters as a side stream into the said device and enters a substantially cylindrical wall : solid particles, accelerated by centrifugal effect, but encountering the said cylindrical wall, lose their kinetic energy, fall under the action of gravity and accumulate at the base of the said cylindrical Enki then removed through the bottom of said device.

In a preferred embodiment of the invention, a rarefaction means is selected comprising at least one solid / gas separation device mounted in the upper part of the upper channel so that the solid particles trapped by the said device can be removed directly into the suspension. For this, the pipeline for removing solid particles held by the said device has a length calculated so that its lower end immerses in the said suspension when it is in a state of potential fluidization. Typically, in the upper part, a standard cyclone contains a cylindrical wall, on the inside of which a lateral slurry jet should fall, a conical wall that converges downward and connects the lower end of the said cylindrical wall with a cylindrical removal pipe, the lower end of which contains an opening through which solid particles are removed. If a standard cyclone is used, it is placed in the upper channel of the duct so that the lower end of the cylindrical pipeline is submerged in suspension in a state of potential fluidization. In the framework of the present invention, a simpler cyclone type device is preferably used in the sense that it does not have a converging conical wall: the cylindrical wall and the removal pipe form a single cylindrical wall, the lower end of which is immersed in the suspension in a state of potential fluidization.

Preferably, in compliance with environmental standards, at least two cyclone-type devices are installed in series in the fluidization gas removal circuit, which makes it possible to ideally clean the gas from dust so that it practically does not contain solid particles larger than 3 micrometers in size. The device or devices of the cyclone type can be standard cyclones, which contain a converging conical wall at the base of the said cylindrical pipeline, but it is preferable to choose special cyclones, which contain a cylindrical wall, the lower part of which is immersed directly in the suspension.

Thanks to the claimed device, it is possible to significantly reduce losses from volatilization. Indeed, in known solutions, the turbulent mode in the expansion columns leads to the volatilization of a large number of particles. The applicant found that stabilization of the upper level of bulk material present in the compensation column (if any), as well as stabilization of the upper level of the layer in the state of potential fluidization in the upper channel, can almost completely eliminate the possibility of volatilization of particles larger than 5 micrometers under normal conditions of use devices. However, even if this is an undoubted advantage, using only the rarefaction means it is not possible to avoid the volatilization of small micrometric and nanometric particles, and often the mentioned rarefaction means must be combined with additional solids / gas separation means.

In the case of refusal to use expansion columns or reduce their number, an advantage of the invention is, on the one hand, simplification of design and manufacture of air ducts and, on the other hand, reduction of energy consumption, since it is much more efficient to use fluidization pressure, providing a bubble in each bubble a pressure much closer to said fluidization pressure.

Mentioned means of creating a vacuum contains at least one hole of a predetermined section, the value of which allows you to create the necessary pressure loss. If this hole is the only outlet for fluidizing gas, it is preferable that the diameter of the hole provide a leakage rate of at least S · u _f , where S is the area of the part of the porous wall corresponding to the bubble in question, and where u _f is the fluidization velocity. Typically, for a material such as metallurgical alumina, the fluidization rate is from 5 to 15 mm · s ^-1 . Thus, for a portion of the duct corresponding to a given vesicle, which will hereafter be called "caisson" section of the porous wall is known, and from it is possible to deduce the gas outlet flow rate which corresponds to the flow S · u _f, and can thus determine the diameter holes, since with a given hole diameter, the classical rules of hydraulics allow us to determine the relationship between the pressure loss and the leakage rate.

The loss of pressure in the hole is essentially proportional to the square of the mass flow rate of the gas leak passing through the hole, and corresponds to the rule of the type:

, где $$\beta =\frac{d_{or}}{d_t}$$

, $$At=\frac{\pi }{4}{d}_t^2$$

$$\Delta P=\frac{\mathrm{one}}{2\rho }{\left[\frac{F_g{(\mathrm{one}-{\beta }^{\mathrm{four}})}^{0,5}}{K{A}_t}\right]}^2$$

where $$\beta =\frac{d_{or}}{d_t}$$

, $$At=\frac{\pi }{\mathrm{four}}{d}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="00000005.png,00000006.png"\; state="\{\{state\}\}">t</figure-callout>}}^2$$

and where

- ΔP is the pressure loss in the hole (expressed in bars: 1 bar = 0.1 MPa),

- d _or is the diameter of the hole,

- d _t is the diameter of the pipe connecting the upper wall of the upper channel with a diaphragm containing the aforementioned hole,

- ρ is the density of the fluidizing air (expressed in kg / m ³ ),

- F _g is the mass flow of fluidizing air (kg / h) ("leakage rate"),

- K is the pressure loss constant.

As an example, consider a duct equipped with a porous wall 14 cm wide. If at the caisson level it is necessary to obtain a bubble pressure of 0.05 bar (5000 Pa) (in this case, expressed as an excess of pressure relative to atmospheric pressure) and a fluidizing gas velocity of 15 mm / s the diameter of the hole through which the upper part of the upper channel communicates with the surrounding air should be 25 mm if the caisson is 12 m long; 34 mm if the caisson is 24 m long; and 46 mm if the caisson is 72 m long.

If the duct section also contains a compensation column, the hole diameter is chosen with a lower value so that the level of suspended solids / gas in the compensation column can be controlled, while simultaneously providing fluidization at a low gas velocity. Returning to the example from the previous section, a well-known caisson equipped with a compensating column and having a typical length of about 6 meters should be equipped with a hole with a diameter of about 20 mm if the compensation column is removed. At the same time, if there is a need to preserve the mentioned compensation column and if this new means of creating vacuum is to be used only to stabilize the upper level of suspension (gas + bulk material) in the compensation column, a hole with a diameter much smaller than 20 mm is made, since the height filling said compensation column with said suspension allows balancing the pressure in the upper channel minus the pressure loss associated with the presence of said opening.

Preferably, the rarefaction means that provides substantially constant bubble pressure, creating a constant pressure loss with respect to the external pressure, is designed so as to obtain a large pressure loss and to avoid too high a height of the upper level of bulk material in the expansion column. Due to the fact that the height of the suspension column of a solid / gas does not exceed a certain value, as a rule, about 1 m, the dimensions, weight and cost of the said expansion columns are limited and at the same time increase the reliability of the transportation system.

Preferably, said opening, such as a valve opening, could have a variable cross-section, which allows you to change the bubble pressure, as well as to make more flexible the local working conditions of the duct or adapt a device of this geometry to transport different bulk materials. In this regard, reference can be made to document WO2009 / 010667, which indicates the region of bulk materials that can be transported in an ultra-dense layer: shown in the Geldart diagram in FIG. 1, where they are characterized by their average particle size and density (in particular, the difference between this density and density of the fluidizing gas), they are preferably located in the shaded area of figure 1 of this document.

Figure 1 depicts a diagram of a known device with a compensation column disclosed in EP 1086035, a view in vertical section.

Figure 2 is a first embodiment of the invention as applied to this device.

Figure 3 is a vertical section of a device according to a variant embodiment of the invention, not equipped with a compensation column.

Figure 4 - in vertical section, a device similar to the previous one and different from it in that at the level of each bubble, the upper wall of the upper channel is equipped with an unloading valve.

5 is a vertical sectional view of another device in accordance with the invention, adapted both for the continuous supply of bulk material from a storage tank and for transporting bulk material over a long distance.

6 is a vertical section of the intermediate section and the end section of the fourth device according to the invention. The intermediate section shown corresponds to the boundary between two adjacent bubbles, indicated by positions with indices i and i + 1. The power supply not shown corresponds to the previous figures, while the flow of material in all the figures conditionally moves from left to right.

EXAMPLES OF IMPLEMENTATION

EXAMPLE 1: Design of a known device (figures 1 and 2)

The device shown in FIG. 1 was described in document EP 1086035. It comprises an external storage tank 1 for transporting material, connected by a pipe 2 to a conveyor 3 of the duct type, removal means 9 from the conveyor, which with the aid of a controlled dosage system 10 directs bulk material into feed zone 11.

The external storage tank 1 contains bulk loose material 12, which is affected by atmospheric pressure. This tank is supported on one end of the horizontal (or inclined) conveyor 3 through the pipeline 2. The conveyor 3 contains a porous wall 5, which separates the lower channel 6 from the upper channel 7, intended for circulation of bulk material.

The fluidizing gas G is supplied through a conduit 8 to the lower channel 6, where it is affected by a fluidization pressure p _f . This gas passes through the porous wall 5, then through the bulk material 12, which fills the upper channel 7 of the conveyor, forming with it a layer 12 'of potential fluidization, that is, a suspension of solid granular particles in the gaseous phase. This potential fluidization layer 12 ′ is in a superdense phase, while in the case of alumina intended for electrolyzers, the suspension has a density of about 900 kg per m ³ . Gas escapes with a small flow rate, passing through bulk material partially filling the compensation column (4.1, 4.2) to a substantially horizontal upper level (15.1, 15.2), while the gauge height (h1, h2) balances at the level of each bubble (20.1, 20.2) gas pressure p _f . Above the upper level 13 of the potential fluidization layer 12 ′, a gas bubble forms under pressure (20.1, 20.2), enclosed in a space formed by the upper wall 14 of the upper channel 7 and the barriers. For bubble 20.1, these barriers are formed by a steel sheet 50, insert 51 of the storage tank and insert 40.1 of the compensation column 4.1. For the bubble 20.2, these barriers are formed by a steel sheet 50, insert 40.2 of the expansion column 4.2 and the upper part of the end side wall 52 of the duct. As a result of creating a fluidization pressure p _f in the lower channel 6 inside the bubbles 20.1 and 20.2, respectively, bubble pressures p _b1 and p _b2 act. In the known device, these bubble pressures can only be changed by changing the fluidization pressure p _f .

As shown in FIG. 2, the previous device was improved in the sense that, according to the present invention, an opening (100.1, 100.2) is made in the upper wall 14 of the upper channel 7 at the level of each bubble (20.1, 20.2) to release fluidizing gas into the surrounding a medium in which a substantially constant pressure acts, while the passage of the fluidizing gas through this opening occurs with a strictly defined pressure loss, depending on the diameter of the said opening. The first consequence of making this hole is to stabilize the position of the upper levels 15.1 and 15.2, that is, the heights h1 and h2 of the volumes of bulk material occupying the expansion columns 4.1 and 4.2, in order to significantly reduce losses from volatilization, without resorting to shaping the upper ends of the said compensation columns. For example, in an experimental device, which, of course, is slightly different from the device shown in Fig. 2, in that it contains only one bubble, to which a discharge valve is connected, the amplitudes of the height variation of the upper level of the bulk material column decreased from several hundred millimeters to several millimeters. In the experimental device, the upper channel had a height of 40 cm. It was equipped in its upper part with a barrier that ensured the formation of a bubble under pressure several centimeters high. The fan used allows you to change the fluidization pressure between 90 and 200 mbar (relative pressure: we are talking about excess pressure relative to atmospheric pressure). Depending on the opening of the discharge valve, the bubble pressure varied from 15 to 100 mbar, the height of the solid / gas suspension column in the compensation column varied between 20 and 100 cm, and the value of this height remained almost stable when the opening of the valve was limited by a given diameter, and the fan worked in a given mode.

Stabilization of the upper level of the compensation column allows almost completely to eliminate the volatilization of particles, the size of which usually exceeds 5 micrometers, under normal conditions of use of the device.

In an embodiment of the device according to the invention, equipped with expansion columns, the holes made in the upper wall of the upper channel have a variable diameter (for example, the arch of each bubble is equipped with an unloading valve). Thus, it is possible to individually change the bubble pressure in each bubble by acting directly on the discharge valve connected to the corresponding bubble, without changing the fluidization pressure.

EXAMPLE 2 (FIGS. 3 and 4)

Example 2 illustrates a device according to the invention, characterized in that it does not contain expansion columns. The bubble pressures p _b1 and p _b2 remain essentially constant at predetermined values due to the pressure losses created by the openings 110.1 and 110.2 with the corresponding diameters D1 and D2 made in the upper wall 14 of the upper channel 7. The holes 110.1 and 110.2 are the inlets of the nozzles 30.1 and 30.2 with diameters at least equal to D1 and D2, respectively, which ensure the removal of fluidizing gas. These exhaust pipes exit to the atmosphere, or preferably, in particular, when it comes to a device for the constant supply of alumina for electrolysis cells, to gas treatment centers.

Thanks to this device, they significantly reduce the losses associated with volatilization. To purify gas from even smaller particles, typically submicron and even nanometric, preferably the fluidizing gas removal pipes 30.1 and 30.2 are equipped with a dust removal device, for example, a cyclone (not shown in FIG. 3). In this case, the inlet of the nozzle 30.1 (30.2, respectively) should have a predetermined section, different from the section that it would have been in the absence of a dust removal device, since the sum of the pressure losses should be equivalent to the vacuum provided by only one hole.

Figure 4 shows a variant of the previous device, which does not contain expansion columns, in which the holes are replaced by discharge valves 120.1 and 120.2, connecting the arch of each bubble 20.1 and 20.2 with a nozzle for the release of fluidizing gas (30.1 and 30.2). The degree of opening of the valve is variable, therefore, changing the diameter of its opening, we can change the bubble pressure at the level of each bubble. The first advantage of such a device is the ability to control and local impact on the flow of material in the conveyor. Another advantage is the ability to perform a device of this geometry, which can be used to transport various materials.

EXAMPLE 3 (Figure 5)

Figure 5 presents another embodiment of the invention, intended, in particular, for transporting bulk material over a long distance in conditions where the fluidizing gas cannot be removed to the gas processing center. In this case, the fluidizing gas removal means comprises a chamber 60 made in the arch of the upper channel 7, inside of which there is at least one gas / solid separation device. In the embodiment illustrated by the present example, two gas / solids separation devices 61 and 62 are installed in series, in this case a cyclone type, in order to satisfy increasingly stringent environmental requirements: dust-free gas contains only an insignificant amount of fine micrometric particles. Each of these devices contains a substantially cylindrical wall 610 and 620, the lower part of which is immersed in a potential fluidization bed, and an inlet pipe configured so that the gas / solid suspension approaches tangentially to the said cylindrical wall. The tangential inlet allows gas / solids to flow along the wall and towards the bottom of the cyclone. The centrifugal force created in this way separates the particles from the gas. Solid particles come into contact with a cylindrical wall, lose part of their kinetic energy and fall under the action of gravity in the direction of the potential fluidization bed. The height of this cylindrical wall is determined so that the solid substance coming directly from the potential fluidization bed does not clog the said cyclone.

The inlet pipe of the first cyclone contains an inlet 130, the diameter of which is calculated so that the inlet speed of the dust-free stream is from 2 to 40 m / s, preferably from 15 to 40 m / s, to ensure maximum separation efficiency. The dimension of each cyclone is determined in such a way that the input diameter adapted for the normal operation of the cyclone contributes to a complete loss of pressure, reaching a predetermined value in the framework of the present invention. The outlet pipe 31 of the aforementioned cyclone type device, which allows fluidizing gas to be removed, is equipped with a discharge valve 131, the variable opening of which allows bubble pressure p _b1 to be controlled.

EXAMPLE 4 (FIG. 6)

The device according to this example, shown in Fig.6, like the previous device, is designed to transport bulk material over long distances. It has two independent preferred features.

The first of these features relates to the configuration of the end caisson 300: instead of containing, as in the first examples, the removal means 9 connected to the bottom of the upper channel, essentially vertical and downward, it is equipped with a substantially vertical upward end column 9 ', into which material can rise under the action of fluidizing gas pressure. A 9 ”tap allows you to remove excess bulk material. An outlet 9 ″ is connected to said end column 9 ′ at a height slightly exceeding the height of the upper wall 14 of the upper channel 7 and selected so that the inset can be below the upper level 15.3 of the suspension of bulk material + gas. Preferably, said end column 9 ′ is closed from above by an upper wall 14 ′ equipped with vacuum means, such as a discharge valve 141, so that a pressure bubble under said upper wall can have a predetermined bubble pressure. This configuration allows you to stabilize in this place the upper level of the layer 12 'of potential fluidization, which contributes to the continuous passage of the flow of transported material with a constant flow rate. Preferably, in this end part, the fluidizing gas is supplied separately to the lower channel zone 6.2 in such a way as to obtain a fluidization pressure p _f2 that is different and, as a rule, higher than the pressure p _f1 in the rest, that is, in almost the entire remaining part 6.1 of the lower channel.

Such a configuration, in which a 9 ”outlet is made over the upper level 15.3 of suspended solids + gas to exit excess material, is most adapted for the flow passing without risk of segregation using the boiling mode proposed in WO2009 / 010667. For materials with a risk of segregation, such as polydisperse bulk materials, preferably at the level of this end caisson provide an outlet located slightly above the porous wall (or mesh) 5.

The second of these features is of exceptional interest, since it allows the bulk material to be transported over a long distance, which gradually rises in height. The duct contains the upper channel, divided into compartments in such a way that it contains n adjacent bubbles under the corresponding pressures p _bi , while i varies from 1 to n. The upper wall 14 of the upper channel is equipped with barriers in the form of transverse walls, such as 50.i and 50.n. Each corresponding bubble 20.i (i = 1 to n) is equipped with a vacuum, in this case, an unloading valve 140.i. Adjacent bubbles 20i and 20. (i + 1) are separated by a barrier 50.i. A pipe 150.i is installed on the channel in the form of an inverted U, hereinafter referred to as a “siphon”, while the U branches are located on both sides of the mentioned barrier 50.i and have a length sufficient for their ends to come into suspension in a state of potential fluidization. The relief valves 140.i and 140. (i + 1) are adjusted so that bubble pressure p _bi exceeding p _{b (i + 1)} acts on both sides of the barrier 50.i. In practice, the discharge valve 140.i located closer to the inlet is open more than the discharge valve 140. (i + 1) located closer to the outlet. Due to this, since the fluidizing gas can escape with a leakage rate lower in the front section than in the rear section, the bubble pressure p _{b (i + 1) is} lower than the bubble pressure p _bi , and a gas flow is established in the siphon (at 6 is shown by a simple arrow), which passes from the front section to the rear section and exits through the rear discharge valve 140. (i + 1). The applicant unexpectedly discovered that this gas stream in said siphon does not entrain solid particles.

Given this bubble pressure difference, the upper level 13.i of the potential fluidization layer in front of the barrier 50.i is at a lower height than the upper level 13. (i + 1) of the potential fluidization layer behind the barrier 50.i. Thus, the upper level of the potential fluidization bed increases with each passage through the barrier 50.i.

It is obvious that the pipe in the form of an inverted U cannot have any section desired: it is necessary that the passage of the fluidizing gas from one bubble to another, which occurs with a mass flow rate corresponding to the difference between the leakage costs of the removal means from these adjacent bubbles, can be close or lower speed of transportation of alumina to limit the volatilization of particles. In fact, in order to achieve the desired effect (transportation of bulk material over a long distance with a gradual increase in its height), it is necessary

a) equip two adjacent bubbles with a means of creating a vacuum so that the vacuum at the exit of the posterior bubble exceeds the vacuum at the exit of the front bubble; and

b) provide a passage between two adjacent bubbles so that it is possible to compensate for the difference in the leakage costs of the removal means from the said adjacent bubbles, the passage being said to be, as a rule, a pipe in the form of an inverted U mounted on the channel so that the branches of U are from two sides from the mentioned barrier 50.i and have a sufficient length so that their ends go into suspension in a state of potential fluidization, must have such a cross section that the fluidizing gas passes through this passage at a speed, b low or lower speed of transportation of alumina.

Claims (20)

1. A device for conveying bulk material (12) between a feed zone (1) and at least one feed zone, comprising a conveyor (3) called an “air duct” that includes a lower channel (6) for gas circulation and an upper channel (7) designed to circulate bulk material and said gas, wherein said lower channel and said upper channel are separated by a porous wall (5) through which said gas can pass, while the lower channel is connected to a gas supply pipe (8) made with possible the supply of said lower channel with gas under pressure p _f , which provides potential fluidization of said bulk material in said upper channel and which is called “fluidization pressure”, while said upper channel is equipped in its upper part with transverse walls (50, 51, 52; 53 ; 50.i, 50.n), which form an obstacle to the circulation of said gas and said bulk material, wherein said transverse walls are arranged in such a way that they form together with the upper wall of said at least one space in which a gas bubble forms under pressure (20.1, 20.2; 20.i, 20. (i + 1), 20.n) having a predetermined bubble pressure as a result of creating a potential fluidization pressure in said duct, wherein said duct consists of caissons, each of which corresponds to a given bubble, wherein said device characterized in that at the level of at least one bubble the wall of the upper channel is equipped with a fluidizing gas removal means connecting the said bubble with the external environment and containing a means of creating a vacuum (100.1, 100.2; 110.1, 110.2; 120.1, 120.2; 130, 61, 62; 140.i, 140. (i + 1), 140.n), which creates an essentially constant vacuum. 2. The device according to claim 1, characterized in that the rarefaction means is designed so that said substantially constant rarefaction created by said means has a meaning such that if the pressure in said external medium is substantially constant, said bubble the pressure is maintained substantially constant between the fluidization pressure p _f and the pressure of said external medium. 3. The device according to claim 1 or 2, characterized in that at the level of each bubble (20.1, 20.2, ..., 20.i, 20. (i + 1), ..., 20.n) the wall of the upper channel is equipped with a fluidization removal means gas connecting said upper channel to said external medium and containing a rarefaction means that creates a substantially constant vacuum. 4. The device according to any one of claims 1 or 2, characterized in that it does not contain a compensation column (4.1, 4.2), that is, a column whose upper end is open to the external environment and which is filled with bulk material so that during pressure potential fluidization in said duct, a suspension containing gas and bulk material, which fills the said compensation column, had a filling height, allowing to balance the pressure present in the said upper channel. 5. A device according to any one of claims 1 or 2, characterized in that said removal means comprises at least one solid / gas separation device. 6. A device according to any one of claims 1 or 2, characterized in that said removal means is said rarefaction means and is made in the form of an opening (100.1, 100.2) adjacent to the envelope of the volume occupied by said bubble, the diameter of which corresponds to a pressure loss, providing the necessary bubble pressure. 7. Device according to any one of claims 1 or 2, characterized in that said fluidizing gas removal means is a nozzle (30.1, 30.2) extending into the upper channel at the level of the bubble, usually into the upper wall of the upper channel, wherein said means of creating rarefaction is the inlet (110.1, 110.2) of the pipe, the diameter of which corresponds to the loss of pressure, providing the necessary bubble pressure. 8. The device according to claim 7, characterized in that the said pipe (30.1, 30.2) is equipped with an unloading valve (120.1, 120.2) containing an orifice of variable diameter, which allows you to change the pressure loss of the gas during its removal. 9. The device according to claim 5, characterized in that said fluidizing gas removal means comprises a chamber (60), which is made in the upper part of the upper channel (7) and inside which there is said gas / solid separation device. 10. The device according to claim 9, in which said gas / solids separation device (61) is a cyclone type device and comprises a pipe for removing solid particles trapped by said device, the length of which is determined so that its lower end is immersed in said suspension when it is in a state of potential fluidization. 11. The device according to claim 9 or 10, wherein said gas / solids separation device (61) comprises an inlet pipe and a substantially cylindrical wall (610), wherein the inlet pipe is configured so that gas with solid particles flows tangentially to said substantially cylindrical wall, wherein the height of said substantially cylindrical wall is determined so that its lower part is immersed in the suspension (12 ') present in the upper channel when it is in a potential pseudo state liquefaction. 12. A device according to any one of claims 9 or 10, wherein said gas / solids separation device comprises an inlet (130) for admitting a gas with solid particles, the diameter of which is calculated so that the inlet velocity of the said gas, intended for cleaning dust, had a value of from 2 to 40 m / s, while the dimension of the aforementioned device is determined so that the diameter of the inlet, adapted for the normal operation of the aforementioned separation device, contributed to the total pressure loss at which oh, the necessary bubble pressure is reached. 13. The device according to item 12, in which the outlet pipe (31) of the said gas / solid separation device is equipped with a discharge valve (131), the variable opening of which allows to control the bubble pressure p _b1 . 14. A device according to any one of claims 9 or 10, wherein said gas / solid separation device consists of several cyclone-type devices installed in series (61, 62). 15. The device according to claim 1, characterized in that it contains an end caisson (300), equipped with a substantially vertical and upwardly directed end column (9 '), into which the material can rise under the action of fluidizing gas pressure, an outlet (9' ') , allowing you to remove excess bulk material, while said outlet (9 '') is connected to the said end column (9 ') at a height slightly exceeding the height of the upper wall (14) of the upper channel (7) and determined so that the inset could be under the upper level (15.3) suspensions containing bulk material and gas. 16. The device according to clause 15, in which the said end column (9 ') is closed on top of the upper wall (14'), equipped with a means of creating a vacuum so that under the upper wall could form a bubble at a given bubble pressure. 17. The device according to clause 15, in which at the level of the said end box (300) in the zone (6.2) of the lower channel, a fluidizing gas is separately supplied so as to obtain a fluidization pressure p _f2 different from the pressure p _f1 present in the rest ( 6.1) the lower channel. 18. The device according to clause 15, in which the lower part of the upper channel of the end caisson (300) is also equipped with a removal tool located slightly above the porous wall (5). 19. Device according to any one of claims 1 or 2, characterized in that the said upper channel (7) is divided into compartments in such a way that it contains n adjacent bubbles (20.1, ..., 20.i, ..., 20.n) located under the corresponding pressures p _bi ; in this case, i varies from 1 to n, while the upper wall (14) of the upper channel (7) is equipped with barriers (50.i, 50.n) separating these bubbles, with each corresponding bubble (20 .i, where i = 1 to n) is equipped with rarefaction means, such as a pressure relief valve (140.i), and with at least two compartments of the upper channel ( 7), corresponding to two adjacent bubbles (20.i, 20. (i + 1)), are equipped with rarefaction means (140.i, 140. (i + 1)) so that the vacuum at the exit of the posterior bubble (20. i) exceeded the rarefaction at the outlet of the front bubble (20. (i + 1)), and that a passage is made between said adjacent bubbles, which makes it possible to compensate for the difference between the leakage costs of the removal means from said adjacent bubbles, wherein said passage has such a section at which the fluidizing gas passes through this passage at a speed close to sludge and lower fluidization rates. 20. The device according to claim 19, in which the said passage is a pipe (150.i) in the form of an inverted U mounted on the duct so that the branches U are on both sides of the said barrier (50.i) and have a length sufficient so that their ends go into suspension in a state of potential fluidization.

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